1. Field of the Invention
The present invention relates to a liquid discharge substrate and a liquid discharge head including the same.
2. Description of the Related Art
A typical liquid discharge system for a liquid discharge head mounted in a liquid recording apparatus that performs recording by discharging liquid, such as ink, uses electrothermal transducers as elements that generate energy for discharging the liquid. The electrothermal transducers generate heat by converting electric energy to thermal energy when an electric control signal for recording is sent thereto. In this system, electrothermal transducers are disposed in the vicinity of the individual discharge ports, and liquid in the vicinity of the electrothermal transducers are heated by the electrothermal transducers and are boiled instantly to generate bubbling pressure, so that the liquid in the vicinity of the discharge ports is discharged through the discharge ports. Thus, a recording medium opposing to the discharge port is subjected to recording.
Such a liquid discharge head generally includes a liquid discharge substrate having a liquid supply port and a support substrate that supports the liquid discharge substrate. The liquid discharge substrate has, on the front surface thereof, a plurality of electrothermal transducers arranged in order and a flow-passage forming member having bubbling chambers that accommodate the individual electrothermal transducers and discharge ports that communicate the bubbling chambers with external space. The individual bubbling chambers communicate with the corresponding ink supply ports.
The front surface of the liquid discharge substrate has electrode terminals and electrodes. The electrode terminals are electrically connected to the electrothermal transducers etc. through the electrodes. The liquid-discharge-head main body transmits electric control signals and supplies driving power to the liquid discharge substrate using an electric circuit of the support substrate that is electrically connected to the electrode terminals on the liquid-discharge substrate.
Since recent ink-discharge recording apparatuses fall in price, manufacturing costs of the liquid discharge heads need to be reduced. To this end, it is considered to make the liquid discharge substrate compact to increase the number of the liquid discharge substrates obtained from one wafer.
However, making the liquid discharge substrate compact reduces the area of the front surface of the liquid discharge substrate on which electrodes can be disposed, which needs to decrease the width of the electrodes. This increases the resistance of the liquid discharge substrate, making it difficult to obtain sufficient power to drive the electrothermal transducers etc. Although the resistance can be reduced by forming thick electrodes, forming the thick electrodes may have problems when forming a flow-passage forming member on the electrodes.
As a method for solving the above problems, through electrodes that pass through the liquid discharge substrate from the back to the front can be proposed. This allows transmission of electric control signals and supply of driving power to the electrothermal transducers etc. formed on the liquid discharge substrate even if part of the electrodes is formed on the back surface of the liquid discharge substrate.
Since the back surface of the liquid discharge substrate is not provided with the electrothermal transducers etc., so that it has a wide area in which electrodes can be disposed, allowing the electrodes to be made wide. Moreover, since the flow-passage forming member is not formed on the electrodes, the electrodes can be made wide. Providing the through electrodes in the liquid discharge substrate in this way can reduce the resistance of the liquid discharge substrate by changing the width or thickness of the electrodes.
Since such a liquid discharge substrate has electrodes formed on the back surface thereof, the electrode terminals of the electrodes are generally provided on the back surface.
PCT International Publication No. WO2006/112526 describes a liquid discharge head fitted with a liquid discharge substrate having electrode terminals on the back surface thereof. FIG. 13 is a cross-sectional view showing electrical connecting portions between the liquid discharge substrate and the support substrate of the liquid discharge head and the vicinity thereof.
The liquid discharge head includes a liquid discharge substrate 100 having an ink supply port 102 and a support substrate 200 having three-dimensional wiring. The support substrate 200 is formed of layered ceramic sheets 201 and has connecting pads 202 on the front surface of the support substrate 200. On the back surface of the liquid discharge substrate 100, electrode terminals 111 are provided. The connecting pads 202 on the support substrate 200 and the electrode terminals 111 on the liquid discharge substrate 100 are electrically connected through bumps 205. Thus, transmission of electric control signals and supply of driving power from the liquid-discharge-head main body to the liquid discharge substrate 100 are performed.
Furthermore, electrical connecting portions in which the connecting pads 202 and the electrode terminals 111 are connected with the bumps 205 are provided. The clearance between the liquid discharge substrate 100 and the support substrate 200 is sealed by a sealing member 206. This prevents leakage of ink from between the liquid discharge substrate 100 and the support substrate 200 and electrical problems due to contact of the electrical connecting portions with ink.
Although the sealing technique of the electrical connecting portions disposed between the two substrates with a sealing member is generally used in various devices, sufficient sealing can generally be achieved by sealing the entire substrates including the electrical connecting portions with a sealing member.
However, the liquid discharge head shown in FIG. 13 is provided with the ink supply port 102 in the proximity of a portion at which the sealing member 206 is disposed. Therefore, if the sealing member 206 enters the ink supply port 102, it hinders supply of ink. Therefore, an excessive amount of the sealing member 206 cannot be disposed between the liquid discharge substrate 100 and the support substrate 200.
On the other hand, if the amount of the sealing member 206 is insufficient, the electrical connecting portions disposed in the proximity of the ink supply port 102 are not sufficiently sealed, so that ink comes into contact with the electrical connecting portions, thus sometimes causing electrical problems.
Thus, this liquid discharge head needs accurate sealing of the very small portion, which makes it impossible to improve the reliability and manufacture yields. Moreover, reducing the size of the liquid discharge substrate decreases the portion to be sealed by the sealing member, which makes it more difficult to achieve accurate sealing.